Thermoplastic compositions of polyphenylene ether(oxide)resin and poly(alkenyl aromatic)resin have been described by Cizek, in U.S. Pat. No. 3,383,435, and elsewhere in the patent literature, and have been known in the art for some time. These compositions are moldable into a wide variety of shaped articles which are characterized by good physical properties but may be unsuitable for some applications because of flammability, principally due to the poly(alkenyl aromatic) portion of the composition. For articles requiring better flame resistance, it has become common practice to add flame retardant agents to the blend of polymers. Many types of such additives have been proposed. Examples include halogenated aromatic compounds, halogenated organic compounds in admixture with antimony oxide, aromatic phosphates, and phosphonate compounds, halogen-containing compounds in admixture with phosphorus compounds, and halogenated polymers, e.g., chlorinated or brominated polystyrene or polycarbonate. Some of the descriptive patent literature includes U.S. Pat. No. 3,809.729 (Reinhard), U.S. Pat. No. 3,639,506 (Haaf), U.S. Pat. No. 4,191,685 (Haaf and Lee, Jr.) and U.S. Pat. No. 4,355,126 (Haaf and Reinhard).
Knoth, Jr. et al. in U.S. Pat. No. 3,975,447 disclose a process for making certain aromatic phosphine oxides which are useful as flame retardants for organic polymers. The process involves reacting a benzylic halide with a diarylhalophosphine, in a basic medium, to produce a benzyl diaryl phosphine oxide.
Cabasso, et al. in U.S. Pat. No. 4,073,754 describe flame resistant polymer alloys which are blends of a phosphorus-containing polystyrene, or polyphenylene oxide and a second polymer selected from among cellulose esters, unsaturated polyester resins and polystyrene resins. The active flame retardant ingredients are, more specifically, phosphonate groups which are pendent on the polystyrene or polypheylene oxide polymer chains, that is, groups of the formula PO(OR)(OR.sub.1), in which R and R.sub.1 are alkyl or aryl.
A difficulty which has been encountered with low molecular weight flame retardant additives, and with triphenyl phosphate and other aromatic phosphates in particular, is that these compounds tend to volatilize when the polymer blend is molded or otherwise processed at elevated temperatures. As a result, significant amounts of the additive may migrate to the surface, where they remain or are lost to the atmosphere. This, in turn, can lead to losses in the flame retardancy and the appearance of unsightly blemishes on the surface of the molded article, either of which is undesirable.